The present invention relates to platinum group metal catalyzed addition-curable silicone adhesive compositions employing an N-heterocyclic silane, such as bis(trimethoxysilyltrimethylene)2,6 pyridine dicarboxylate, as an adhesion promoter.
As shown by Kasuya, U.S. Pat. No. 3,284,406, the adhesion of a cured platinum catalyzed addition-curable silicone composition onto a substrate is achieved by effecting the cure of the silicone composition at a temperature such as 100.degree. C. for at least one hour.
Mitchell et al, U.S. Pat. No. 5,164,461, which is incorporated herein by reference, is directed to the use of certain silylmaleates, silylmaleimides or silylfumarates, such as bis[3-(trimethoxysilyl)alkyl]fumarates as adhesion promoters in addition-curable silicone adhesive compositions. Although the addition-curable silicone compositions of Mitchell et al have been found to be self-bonding to various substrates, such as plastics, metals or glass, these silicone adhesive compositions also require a temperature of about 100.degree. C. to about 150.degree. C. to effect a satisfactory cure.
It would be desirable therefore to provide an addition-curable silicone adhesive composition which could be applied onto an unprimed substrate, such as plastic or metal to effect a satisfactory cure in less than an hour and at a temperature of less than 100.degree. C. In addition, it also would be desirable to produce a silicone substrate composite having a silicone layer which would fail cohesively instead of adhesively when tested. As used hereinafter, the expression "adhesive failure" means the silicone layer can be cleanly separated from the substrate, while in a "cohesive failure", rupture can occur in the silicone layer or in the substrate when separation is achieved.